When sharing an ext storage mount point, it will now use the name of the
mount point instead of an empty string for the target path.

Directory seperator is \ on windows
However we can just check for path != dirname(path) because that is
the same for '' (empty string), '.' and DIRECTORY_SEPARATOR on all OS

To make sure that the dynamic mount config and config classes from
external storages are tested, these are now added into the autotest.sh
test run by enabling the app.

load image via javascript and use $(document).width() to determine the proper side of the image to be returned

Images on public sharing get downscaled to increase use experience - this will speed up loading time

- adding keep aspect to core/ajax/preview.php
- remove duplicate method Preview::show()
- no more hard coded mimetype of preview
- remove .png from the preview urls
- keep old route preview.png for backwards compatibility
- aspect preserving previews are now cached

It turns out that the sharing dropdown is embedded into the table row
for some reason.

This fix makes use of a more specific selector for the checkboxes and
file name links to make sure it doesn't spill into any other potential
elements like the sharing dialog.

Fixed drag and drop code to use FileList.getSelectedFiles() instead of
the visible DOM elements.

Now using _.bind() for event handlers so we can use "this" which is more
readable than a static access to FileList.